1. Field of the Invention
The present invention relates to a magnetoresistance-effect thin film head and, more specifically, to a magnetoresistance-effect thin film head capable ensuring high reliability even in operation in a high-temperature, high-humidity environment.
2. Description of the Prior Art
FIG. 12 shows a previously proposed magnetoresistance-effect thin film head A comprising a substrate 1, a magnetic field sensing element 2, i.e., a magnetoresistance-effect element (hereinafter referred to as "MR element") formed on the substrate 1 perpendicularly to the sliding surface a of a magnetic recording medium, a conductive layer having electrodes 3A and 3B connected to the front and rear ends of the MR element 2 to supply a sense current to the MR element 2 in the direction of a signal magnetic field created by the magnetic recording medium. The thin film head A employs a bias magnetic field creating conductor (hereinafter referred to simply as "bias conductor") 5 formed on an insulating layer 4 formed over the MR element 2 so as to extend across the MR element 2 as means for applying a bias magnetic field. An optimum bias magnetic field can be created by varying the current flowing through the bias conductor 5. In FIG. 12, indicated at 6 is an insulating layer, at 7 is a magnetic shielding layer formed over the MR element to enhance the resolution, and l.sub.1 is a gap. The construction of the MR element 2 consisting of two magnetic films 2b and 2c, and an intermediate layer 2a formed between the magnetic films 2b and 2c is able to avoid perfectly the generation of Barkhausen noise, namely, noise attributable to domain wall displacement.
However, in fabricating the thin film head A of FIG. 12, the bias conductor 5 and the electrode layer having the electrodes 3A and 3B need to be formed separately. Therefore, the thin film head A has a complicated multilayer structure and has difficulty in reducing the gap to increase line recording density.
On the other hand, since a sense current is supplied in a direction perpendicular to the sliding surface a for the foregoing thin film head provided with the two-layer MR element 2, the electrodes 3A and 3B of the MR element 2, and the bias conductor 5 can be formed simultaneously as shown in FIG. 13 (Japanese Patent Laid-open (Kokai) No. 1-116912). This thin film head B can be constructed so that the gap l.sub.2 thereof is smaller than the gap l.sub.1 of the thin film head A of FIG. 12 (l.sub.1 &gt;l.sub.2). However, the size of the MR element 2 of the thin film head B of FIG. 13 must be reduced to increase the recording density, and hence the contact areas and widths of the electrodes 3A and 3B cannot be increased. Therefore, if the electrodes 3A and 3B of the MR element 2, and the bias conductor 5 are formed simultaneously, heat and noise increase due to increase in the resistance. Furthermore, since the width of a portion of the bias conductor 5 extending over and across the MR element 2 is small, the bias conductor 5 is unable to apply a bias magnetic field uniformly to the MR element 2.
The electrodes 3A and 3B of the foregoing thin film head provided with the MR element 2 having one side exposed in the sliding surface a, and the front electrode 3A having one side exposed in the sliding surface a are formed, in most cases, of a metal having a comparatively low resistance, such as Au, Cu or Al, to suppress heat generation and noise generation. However, Au is expensive and is liable to come off the MR element 2 during machining for forming the sliding surface a because Au is soft and inferior in adhesive property, Cu is readily oxidized, inferior in moisture resistance and corrosion resistance, and unreliable in use in a high-temperature, high-humidity environment, and the same may be said of Al.